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  • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
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  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
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  • C30B29/403—AIII-nitrides
  • C30B29/406—Gallium nitride
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  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/60—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape characterised by shape
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Definitions

• the present invention relates to the development of self-supported substrates of nitrides of elements III, and in particular of gallium nitride.
• a self-supported substrate in English "free standing" is a substrate of such thickness that it does not require a support to be used in the manufacture of optoelectronic and electronic components.
• Hetero-epitaxy still remains the only solution for the manufacture of components based on element III nitride.
• the substrates used industrially for the epitaxy of gallium nitride are sapphire (Al 2 O 3 ) and silicon carbide (SiC).
• the differences in lattice parameters and thermal expansion coefficients between these substrates and the element III nitride result in the formation of numerous defects in the epitaxial layers, which degrades the performance of the electronic components produced with these materials.
• the substrate is sapphire, techniques have been developed, which consist in interposing between the substrate and the epitaxial layer of element III nitride a nucleation layer, for example formed of GaN or of AIN deposited with conditions distinct growth. This surface treatment makes it possible to limit the density of defects.
• Such self-supporting GaN substrates typically have a thickness of 300 ⁇ m.
• Document EP 1 041 610 thus discloses such a technique, suitable for specific substrates of the Si, NdGaO 3 or GaAs type.
• the document US2003 / 0014472 describes a technique implementing a chemical attack in the particular case of a LiALO substrate.
• this technique is not applicable for a sapphire substrate, which is chemically inert.
• the use of substrates which can be attacked chemically is not always compatible with the epitaxy techniques conventionally used for depositing thick layers of nitrides of elements III.
• the use of silicon substrates results in the appearance of a thermal stress in tension in the layers of gallium nitride. The latter is responsible for the formation of cracks. What is more, the silicon is not thermally stable at the usual epitaxy temperatures. Methods involving an intermediate step of chemical attack have also been described; this attack being intended to eliminate intermediate layers or sacrificial layers.
• the document US Pat. No. 5,919,305 can thus be cited, where the sacrificial layer, arranged to be partially or totally attacked, can be silicon oxide, silicon nitride, silicon carbide or silicon and where the main objective is to address the problem of thermal expansion mismatch responsible for the high density of defects directly in the epitaxy reactor.
• 6,559,075 is based on the use of a pulsed UN laser emission which passes through the sapphire, but which is absorbed at the level of the Ga ⁇ layer, causing local thermal decomposition of Ga ⁇ near the interface.
• Other documents using this technology can also be cited, including document US2002 / 0182889 or even document US 6,071,795.
• document WO03 / 062507 relates to a process for the preparation of a self-supporting substrate made of a semiconductor material by a technique of bonding a nucleation layer (by “molecular” adhesion) on a substrate. , prior to a step of epitaxy of a monocrystalline layer of said semiconductor material. This nucleation layer playing the role of spontaneously detachable interface under the effect of the decrease in the post-epitaxy temperature, inducing mechanical stresses at this interface.
• the object of the invention is to propose a method for producing a self-supported substrate of element III nitride, which is simple, rapid, inexpensive and which provides a film of element III nitride of good quality, planar and over a large area.
• the subject of the invention is a process for producing self-supported substrates of element III nitride and in particular GaN from a starting substrate, by deposition of element III nitride by epitaxy, characterized in that it includes the use, on said substrate, of an intermediate layer based on silicon, as a sacrificial layer intended to be spontaneously vaporized during the subsequent step of epitaxy of the nitride of element m.
• the process according to the invention is particularly suitable for gallium nitride as element III nitride. It is also possible to make substrates of AIN, Al x Ga 1-x N, In x Ga ⁇ _ x N and more generally Al x Ga y In 1-xy N (with 0.â + y ⁇ ) according to the method of the invention.
• the solid starting substrate can be any material whose chemical and physical properties are compatible with the epitaxy of nitrides of element III and which allows the deposition of a monocrystalline layer of nitride of element LTI.
• the substrate on which the sacrificial layer is deposited must preferably be stable (no decomposition too fast) under the standard growth conditions used for the epitaxy of the nitrides of elements III.
• Mention may in particular be made, as starting substrate, of sapphire (Al 2 O 3 ) or silicon carbide (SiC).
• sapphire is preferentially used as initial substrate.
• the starting substrate can itself be composed of different materials.
• Other thermally and chemically stable substrates can also be used for implementing the method according to the invention, among which it is possible to cite in a non-exhaustive manner, MgAl O 4 , AIN, GaN, quartz or a combination of these latter.
• the intermediate layer, called sacrificial, based on silicon is advantageously doped or undoped silicon.
• silicon-based layer is understood to mean any layer mainly consisting of silicon.
• silicon-based semiconductors with good evaporation can also be used for this purpose.
• the thickness of the sacrificial layer based on silicon can be between 100 nm and 10 ⁇ m.
• the spontaneous vaporization of the sacrificial intermediate layer during the step of epitaxy of nitride of element III has the major advantage of not requiring an additional process step specifically dedicated to the separation of the substrate and the epitaxial layer of element nitride III. In other words, the separation is carried out totally or in great majority in situ, in the reactor intended for the epitaxial growth of the nitride of element III.
• another advantage relating to the method according to the present invention is the reduction of the stresses which cause dislocations, but also of the curvature of the nitride substrate of element III thus obtained, due to the presence of the silicon-based intermediate layer which has a compilable and ductile character.
• the element III nitride which is deposited may or may not be doped. Mention may in particular be made, as doping substances, of magnesium, zinc, beryllium, calcium, carbon, boron, chromium, silicon and iron.
• a monocrystalline silicon layer oriented in the direction ⁇ 111> deposited on the substrate will be chosen.
• Other orientations of silicon can however be implemented in the context of the present invention.
• the monocrystalline layer of silicon can also be oriented in the directions ⁇ 110> and ⁇ 100>.
• the favorable growth conditions for this type of deposit are generally achieved by vapor phase epitaxy (NPE).
• NPE vapor phase epitaxy
• the manufacturing variants of such a deposit, such as bonding of the silicon layer, and not its epitaxy, can also be used.
• bonding techniques can be found in the article "Semiconductor wafer bonding", Sciences and Technology, QY Tong, U. Gos ⁇ le, Wiley Interscience Publications.
• the thickness of the sacrificial layer is advantageously between 100 nm and 10 ⁇ m to allow optimal epitaxy of the final element III nitride layer.
• the silicon-based intermediate layer can be continuous or discontinuous according to a particular geometry (i.e. in an ordered fashion) or else discontinuous without any particular organization (i.e. disordered discontinuous).
• the deposition of element III nitride on the substrate / sacrificial layer assembly can be carried out either from the sacrificial layer, or from the areas of the solid substrate not covered. by the sacrificial layer, or even over the entire surface of the uncovered substrate and of the sacrificial layer.
• the sacrificial layer based on silicon deposited on sapphire or any other compatible substrate, as previously mentioned, can be used as a substrate for the epitaxy of nitrides of elements III.
• a step of depositing a nucleation layer can be carried out before proceeding to the step of epitaxy of the thick layer of nitride of elements III.
• the nature of this nucleation layer is chosen so as to:
• sacrificial layer plays the role of momentary protective layer for the sacrificial layer (the usual nitride growth conditions risk being corrosive for this layer; this is for example notorious in the case where the sacrificial layer is silicon),
• the mesh parameter of the nucleation layer must be compatible with the deposition subsequent layer of element III nitride which will constitute the future self-supporting substrate.
• a nucleation layer is preferably used, the lattice parameter of which is close to that of element III nitride so as to ensure subsequent deposition of monocrystalline element III nitride and to minimize the formation of dislocations.
• nucleation layer it is possible to choose from the group consisting of AIN, SiC, low temperature GaN, Al GaN, Al x Ga y In ⁇ -xy N (where 0 ⁇ + y ⁇ ), Al O 3 , Al As, GaAs or the combination of these different layers.
• the growth of the nucleation layer is preferably done by OrganoMetallic Vapor Phase Epitaxy (EPVOM) at a growth rate of between 0.01 and 3 ⁇ m / h.
• the epitaxy temperature is advantageously less than 1200 ° C. so as not to damage the silicon layer during this first step.
• MLE molecular beam epitaxy
• the deposition of the thick layer of element III nitride is carried out in two stages: a slow initial stage, just after the nucleation layer, is carried out so as to condition optimal crystallinity and a second rapid deposition step which will allow the thickening of the material leading to the future self-supported substrate of element III nitride.
• the initial layer is advantageously deposited by EPVOM, at a speed which can preferably be between 0.1 and 5 ⁇ m / h.
• the EJM technique can also be used.
• the thicknesses of the nucleation layer and of the optional initial element III nitride layer may be between 0.01 and 0.5 ⁇ m and between 0.1 and 10 ⁇ m respectively.
• the layer of element nitride LTI epitaxied in the second step on the initial layer of element III nitride is produced by vapor phase epitaxy (VPE) until a final thickness sufficient for this layer to be separable sapphire substrate without breaking.
• VPE vapor phase epitaxy
• this thickening step is carried out at high speed (generally between 10 and 200 ⁇ m / h) and, to be carried out at low cost, the technique called Epitaxy in the Steam Hydride Phase (HVPE) will be very advantageously used.
• the epitaxy is continued until the layer of element III nitride reaches at least 50 ⁇ m, a thickness conventionally considered sufficient for the self-supported substrate to be “ manipulable ”.
• the self-supporting substrates of GaN typically have a thickness varying from 300 ⁇ m to 1 mm in the case of self-supported substrates with a diameter of 2 ". The minimum thickness is in fact that for which the substrate is sufficiently solid to be handled under normal conditions of use.
• the growth conditions temperature, total pressure in the reactor, atmosphere, growth rate, etc.
• the vaporization of the silicon-based semiconductor must be slow enough to not to disturb the course of the growth of thickening of the layer of element III nitride until its te
• the thickness of the intermediate layer necessary between the substrate and the element III nitride layer depends on the growth conditions used for the thickening of the element III nitride layer.
• the vaporization of an intermediate layer based on silicon could begin to occur during the initial step of low-speed deposition of the element III nitride, that is to say during the EPVOM step. or EJM, and would continue during the thickening step in HVPE. This vaporization risks being all the more rapid the higher the temperature and / or the pressure of the reactors.
• the growth parameters most suitable for the growth of the thick layer of element III nitride as well as for the separation, taken separately or advantageously in combination, are the following: The pressure is between 10 2 and 10 5 Pa, - The temperature is between 800 ° C and 1200 ° C, - The growth rate is between 10 and 200 ⁇ m / h.
• the method has two advantages.
• the first advantage is that the vaporization phenomenon occurs at all identical points on large surfaces.
• the second advantage is that the material obtained is considerably unstressed due to the gradual de-cohesion of the substrate during thickening at high temperature as the intermediate layer based on silicon vaporizes. This leads to obtaining a final layer of quasi-planar element III nitride with minimum curvature.
• the invention relates to a process for the manufacture of a monocrystalline self-supported HT element nitride substrate comprising the following successive steps: (i) depositing or bonding on a substrate a silicon-based sacrificial layer, (ii ) the deposition of a nucleation layer, (iii) the deposition by epitaxy of a thick layer of element III nitride on the bi-layer ⁇ intermediate layer based on silicon / nucleation layer ⁇ , under operating conditions compatible with spontaneous vaporization of the sacrificial layer based on silicon.
• - Figure 2a is a representation of the substrate 1 provided with a sacrificial layer 2 based on silicon entirely covering the substrate 1, on which is deposited a nucleation layer 3
• - Figure 2b is a representation of the substrate 1 provided successively with '' a sacrificial layer 2 based on sihcium not entirely covering the substrate 1 and with a nucleation layer 3 which is epitaxially only on the discontinuous layer 2
• - Figure 2c is a representation of the substrate 1 successively provided with a layer sacrificial 2 based on silicon not entirely covering the substrate 1 and with a nucleation layer 3 which is epitaxially only on the solid substrate 1 from the areas not covered by the sacrificial layer 2
• - Figure 2d is a representation of the substrate 1 provided successively with a sacrificial layer 2 based on silicon which does not entirely cover the substrate 1 and with a nucleation layer 3 which is epitaxied on the sacrificial layer 2 as well as on the parts not
• FIG. 5 is a representation of the substrate at the end of the process, where the sacrificial layer 2 is almost completely vaporized.
• This figure shows the result of the process: namely on the one hand a thick flat self-supporting layer and of large surface (with possible residues of the sacrificial layer on the rear face) and on the other hand the starting substrate 1, potentially covered residue but recyclable.
• FIG. 6 is an illustration of the phenomenon of vaporization of the surface of a solid silicon substrate during the growth of a layer of GaN by EPVOM on top, described in example 1. It should be noted that the diagrams do not are not shown to scale.
• the solid substrate 1 must allow the deposition of a monocrystalline sacrificial layer. This implies that the solid substrate 1 must preferably be monocrystalline in the case where the sacrificial layer 2 is epitaxied on the substrate 1.
• the solid substrate 1 is advantageously sapphire (Al 2 O 3 ) or silicon carbide (SiC) because they have thermal expansion coefficients close to the nitrides of elements m and are chemically stable.
• the optimal thickness of the solid substrate 1 is that of standard substrate: it is between 150 ⁇ m and 1000 ⁇ m for a substrate with a diameter of 2 ". Preferably it can be between 300 ⁇ m and 500 ⁇ m.
• the crystalline orientation of the solid substrate 1 is preferably C (0001) or
• the intermediate layer 2 which serves as a sacrificial layer is a layer of silicon.
• the sacrificial layer 2 is silicon
• the epitaxy on sapphire (0001) gives a silicon crystal (111) whose surface has a hexagonal atomic arrangement, suitable for the epitaxy of element III nitride oriented according to (0001) .
• the sacrificial layer 2 is monocrystalline with the best possible structural quality. Its crystalline structure should approach that of the solid material preferably.
• a sacrificial layer 2 whose epitaxy face has hexagonal symmetry, such as for example a crystal oriented in the direction ⁇ 111>.
• layers oriented in the directions ⁇ 100> or ⁇ 110> can be used. Indeed, it is inter alia possible to epitaxial nitrides of JJI elements with a hexagonal structure on such sacrificial layers, despite the absence of hexagonal symmetry of the layer serving as a substrate.
• a preferred variant of the invention consists in using a sacrificial layer 2 of silicon oriented in the direction ⁇ 111> bonded to a substrate 1, and not epitaxial.
• the substrate 1 does not need to be monocrystalline, unlike the sacrificial layer 2 which is preferably monocrystalline. It is thus possible, for example, to propose the following solid monocrystalline or polycrystalline substrates 1: AIN, GaN, Al 2 O 3 , SiC, quartz.
• the thickness of the sacrificial intermediate layer 2 is preferably between 0.1 and 5 ⁇ m. The optimal thickness depends on the growth conditions used for the epitaxy of the future substrate 4 of element III nitride. The higher the growth temperature, the greater the thickness of the sacrificial layer to avoid too rapid separation of the growing layer 4 and the substrate 1. Similarly, it will be advantageous to increase the thickness of the sacrificial layer 2 for high growth pressure.
• nucleation layer 3 deposited on the sacrificial layer 2, to allow better deposition of the thick layer 4 of element III mtrure which will become the self-supporting substrate.
• the thickness of the nucleation layer 3 is preferably between 10 nm and 50 nm.
• the growth of the nucleation layer is preferably carried out by EPVOM at a growth rate of between 0.1 and 3 ⁇ m / h.
• the epitaxy temperature is advantageously between 900 ° C and 1100 ° C and the pressure below 5 ⁇ 10 4 Pa so as not to evaporate the silicon layer 2 too quickly while retaining a high crystalline quality of the epitaxial layers.
• EJM molecular beam epitaxy
• a variant of the invention consists in depositing the nucleation layer 3: Either exclusively on the sacrificial layer 2.
• the nucleation layer is not continuous and a plane element III nitride layer is obtained in the last thickening step by HVPE, Either exclusively on the parts of the substrate 1 not covered by the sacrificial layer.
• HVPE high vacuum chemical vapor deposition
• the epitaxial relationship between the substrate and the nucleation layer can be used to increase the crystalline quality of the nucleation layer. 3, without calling into question the separation of the nitride layer of element III from the starting substrate 1 during the vaporization of the sacrificial layer 2. Either over the entire surface of the sacrificial layer 2 and of the bare parts of the substrate 1.
• the preferred conditions used for the last step of the process for manufacturing the nitride of element LU and which relates to the deposition of a thick layer 4 of nitride of element III and its separation from the starting substrate by evaporation of the sacrificial layer are developed here.
• the most suitable growth technique is epitaxy in the vapor phase with hydrides (HVPE) because it allows growth rates which can exceed 100 ⁇ m / h ( much higher than the average of 3 ⁇ m / h recommendable in EPVOM) without loss of crystalline quality.
• an epitaxy of GaN by HVPE from a starting layer of GaN epitaxied by MOVPE on sapphire leads to a layer having a dislocation density which decreases with thickness h deposited according to a power law h " (see article by SK Mathis, Jnl. Cryst. G. 231, 371 (2001)) due to the crossing and the annihilation of dislocations.
• a thick layer of 300 ⁇ m has a average dislocation density of 10 7 cm "2 and a thick layer of 1000 ⁇ m has an average dislocation density of 4x10 6 cm " 2.
• One step ELO can possibly further reduce the dislocation density (by at least a factor of 10).
• the partial or total vaporization of the sacrificial layer 2 occurs during the epitaxy of the thick layer 4 of element III nitride which will subsequently become the substrate.
• the optimal growth conditions for element III nitrides by VPE are compatible with the spontaneous vaporization of silicon. It is preferable not to evaporate the sacrificial layer 2 too quickly so as not to disturb the growth of the element III nitride and not to separate the growing layer from the substrate too quickly so as not to break the nitride layer. element III.
• a temperature between 900 ° C and 1100 ° C and a pressure between 10 2 Pa and 10 5 Pa allow optimal growth of layer 4 of nitrides of elements III and an optimal vaporization rate for a sacrificial layer 2 of silicon.
• an additional chemical etching step of the layer 2 based on silicon may prove to be useful for eliminating this silicon entirely from the element III nitride substrate.
• the chemical attack can be carried out according to techniques known from the state of the art. It is preferably carried out at low temperature when the material obtained is discharged from the epitaxy reactor.
• the chemical solution depends on the type of intermediate layer: for silicon, the HNO 3 : HF mixture or KOH is generally used.
• the self-supported GaN layers obtained according to the method of the invention are of great interest for the manufacture of electronic or optoelectronic components such as laser diodes, light emitting diodes, photodetectors, transistors, etc. This is particularly true thanks to the specificity of the process which considerably minimizes the stresses in the material usually created during epitaxy and cooling, and subsequently to minimize the curvature of the element III nitride substrate obtained, typically to reach a radius of curvature greater than 5 m. In particular, the radius of curvature can be close to or exceed 10 m. Another advantage of the process according to the invention is that the starting substrate can be reused several times after separation of the GaN layer, repolishing may prove to be necessary after each use.
• the invention also relates to a self-supported substrate of element III nitride capable of being obtained according to the method of the invention, characterized in that its diameter is greater than or equal to 2 "and in that it has a radius of curvature greater than 5 m.
• the self-supported substrate of element nitride which can be obtained according to the method of the invention has a diameter greater than or equal to 2 "and has a radius of curvature greater than or equal to 10 m.
• Example 1 Method by MOCVD HVPE on sapphire C.
• a self-supported substrate of gallium nitride is produced according to the method of the invention.
• the starting substrate consists of a layer of silicon of 2 ⁇ m oriented in the direction (111) epitaxy by CVD on a sapphire substrate (Al O 3 ) oriented according to (0001) 430 ⁇ m thick and 2 "in diameter.
• the width at mid-height in scanning ⁇ / 2 ⁇ by X-ray diffraction of the silicon layer is of the order of 400 arcsec.
• the first stage of growth of gallium nitride is carried out by EPVOM.
• FIG. 6 illustrates the vaporization of silicon in the practical case of the deposition by EPVOM of GaN / AIN on a solid substrate of
• the thickness deposited by HVPE is 500 ⁇ m. The higher the thickness, the more the crystalline quality of the deposited material increases, always through a process of progressive elimination of dislocations which cross and annihilate each other.
• the typical dislocation density measured is 5x10 6 cm "2 , which corresponds to the expected value following a thickening of 500 ⁇ m by HVPE.
• This dislocation density is therefore equivalent to that obtained for other substrate manufacturing techniques of self-supporting GaN (example: separation by laser ablation).
• the separation of the thick layer of GaN and the sapphire substrate is observed after HVPE growth over the entire surface (2 "). Only a few traces of silicon remain on the rear face of the self-supporting nitride layer; these traces can be eliminated by chemical attack.
• the width at mid-height in scanning ⁇ / 20 by X-ray diffraction for the GaN substrate obtained is less than 100 arcsec.
• the width at mid-height of the excitonic lines (D ° X, A, C) observed by photoluminescence are less than 1 meV.
• Example 2 method by EJM / HVPE on sapphire C.
• a self-supported substrate of gallium nitride is produced according to the method of the invention.
• the starting substrate consists of a silicon layer of 5 ⁇ m oriented in the direction (111) epitaxy by CVD on a sapphire (Al O 3 ) substrate oriented according to (0001) 430 ⁇ m thick and 2 "in diameter.
• the first gallium nitride growth step is carried out by EJM
• the nucleation layer of AIN is deposited at high temperature after annealing / deoxidation of the silicon layer under vacuum at high temperature (850 ° C).
• the thickness of the AIN layer is 30 nm.
• the first layer of GaN is deposited on the nucleation layer at low growth rate (l ⁇ m / h). The thickness of this layer is approximately 500 nm.
• the crystalline quality increases with the thickness deposited (the dislocations cross and annihilate each other).
• the thickness deposited by HVPE is 1000 ⁇ m. The higher the thickness, the more the crystalline quality of the deposited material increases, always through a process of progressive elimination of dislocations which cross and annihilate each other.
• the thick layer of GaN and the sapphire substrate are separated after HVPE growth over the entire surface (2 "). Only a few traces of silicon remain on the rear face of the self-supporting nitride layer; these traces can be eliminated by chemical attack.
• Example 3 process on SiC substrate.
• a self-supported substrate of gallium nitride is produced according to the method of the invention.
• the starting substrate consists of a 0.5 ⁇ m silicon layer oriented in the direction (111) epitaxy by CVD on a 6H-SiC type silicon carbide substrate, oriented according to (0001), with a thickness of 280 ⁇ m and 2 "diameter.
• the first stage of growth of gallium nitride is made by EPVOM.
• the nucleation layer of AIN is deposited at high temperature after annealing / deoxidation of the layer of silicon under H 2 flux for 10 min.
• the thickness of the AIN layer is 50 nm.
• the first layer of GaN is deposited on the nucleation layer at low growth rate (1.5 ⁇ m / h). The thickness of this layer is approximately 1 ⁇ m.
• the thickness deposited by HVPE is 1000 ⁇ m.
• the separation of the thick layer of GaN and the sapphire substrate is observed after HVPE growth over the entire surface (2 "). Only a few traces of silicon remain on the rear face of the self-supporting nitride layer; these traces can be eliminated by chemical attack ..
• Example 4 Process on Sapphire-plane R substrate A self-supported substrate of gallium nitride is produced according to the process of the invention.
• the starting substrate consists of a layer of silicon of 2 ⁇ m oriented in the direction (100) epitaxy by CVD on a sapphire (Al O 3 ) substrate oriented according to (10-12) 430 ⁇ m thick and of diameter 2 ".
• the first stage of growth of gallium nitride is made by EPVOM on an intermediate layer of AIN.
• the AIN nucleation layer is deposited at high temperature after annealing / deoxidation of the silicon layer under N 2 flux for 5 min.The thickness of the AIN layer is 100 nm.
• the first layer of GaN is deposited on the nucleation layer at low growth rate (1.5 ⁇ m / h).
• the thickness deposited by HVPE is 500 ⁇ m.
• the separation of the thick layer of GaN and the sapphire substrate is observed after HVPE growth over the entire surface (2 "). Only a few traces of silicon remain on the rear face of the self-supporting nitride layer; these traces can be eliminated by chemical attack.
• Example 5 ELO use (strips) from an AIN layer
• a self-supported substrate of gallium nitride is produced according to the method of the invention.
• the starting substrate consists of the following stack: a layer of silicon of 1 ⁇ m oriented in the direction (111) epitaxy by CVD on a layer of AIN of 50 nm deposited on a layer of GaN of 2 ⁇ m on a substrate of sapphire (Al 2 O 3 ) oriented along (0001) 430 ⁇ m thick and 2 "in diameter.
• the AIN layer serves as a protective barrier between the silicon layer and the GaN layer which can react together and degrade (diffusion of silicon in GaN).
• a 200 nm SiO 2 layer which will serve as a mask is deposited on the silicon layer. Patterns formed by bands a few microns wide separated by several microns (typically 5 ⁇ m / 5 ⁇ m) are revealed in the SiO 2 layer by a standard photolithography step and a chemical attack by BOE for 3 min. Then a chemical attack on the silicon layer by KOH at 80 ° C for 10 min is used to etch the layer unmasked silicon up to the AIN layer (with the same pattern as that defined by photolithography). A first step of regrowth of gallium nitride is made by EPVOM at the openings of the silicon layer from the AIN layer.
• the deposition of GaN is done to obtain a continuous and preferably flat layer before growth by HVPE using a well-known growth technique called ELO.
• the thickness of GaN deposited is 2 ⁇ m.
• This ELO regrowth step allows a reduction in the dislocation density of 1 to 2 orders of magnitude in the GaN layer deposited in the first step.
• the thickness deposited by HVPE is 500 ⁇ m.
• the separation of the thick layer of GaN and the sapphire substrate is observed after HVPE growth over the entire surface (2 "). Only a few traces of silicon remain on the rear face of the self-supporting nitride layer; these traces can be eliminated by chemical attack.
• the dislocation density measured is less than 5x10 6 cm "2 thanks to the use of the ELO technique.
• Example 6 ELO use (holes) from a GaN layer
• a self-supported substrate of gallium nitride is produced according to the method of the invention.
• the starting substrate consists of the following stack: a layer of 1 ⁇ m silicon oriented in the direction (111) CVD epitaxy on a 50 nm AIN layer deposited on a 2 ⁇ m GaN layer on a sapphire (Al 2 O 3 ) substrate oriented (0001) 430 ⁇ m thick and 2 "in diameter.
• a 20 nm layer of SiN which will serve as a mask is deposited on the silicon layer.
• Patterns formed by holes a few microns in diameter, separated by several microns (typically 5 ⁇ m / 15 ⁇ m), are revealed in the SiN layer by a standard photolithography step and a plasma attack (RIE) using for example Cl 2 or O 2 gases. Then a chemical attack on the silicon layer by KOH at 80 ° C for 10 min is used to etch the silicon layer to the AIN layer with the same pattern as that defined by photolithography. Finally the AIN layer is etched to the GaN layer by RIE ( plasma Cl 2 ). A first stage of growth of gallium nitride is made e by EPVOM at the openings of the silicon layer from the GaN layer.
• RIE plasma attack
• the deposition of GaN is done to obtain a continuous and preferably flat layer before growth by HVPE using a well-known growth technique called ELO.
• the thickness of GaN deposited is 2 ⁇ m.
• the thickness deposited by HVPE is 500 ⁇ m. The separation of the thick layer of GaN and the sapphire substrate is observed after HVPE growth. only
• Example 7 ELO use from sapphire
• the starting substrate consists of a layer of silicon of 1 ⁇ m epitaxy by CVD on a sapphire substrate (Al O 3 ) oriented along (0001) of 430 ⁇ m thickness and diameter 2 ".
• a layer of SiO 2 of 200 nm which will serve as a mask is deposited on the silicon layer.
• Patterns formed by bands of a few microns wide separated by several microns are revealed in the SiO 2 layer by a standard photolithography step and a chemical attack by BOE for 3 min Then a chemical attack on the silicon layer by KOH at 80 ° C for 10 min is used to etch the silicon layer to the sapphire substrate with the same pattern as that defined by photolithography.
• a first stage of gallium nitride growth is made by EPVOM at the openings of the silicon layer from the sapphire substrate at low temperature (600 ° C) to obtain a homogeneous deposit over the entire surface. eur of this GaN layer is about 30 nm.
• an annealing is done at standard growth temperature (1090 ° C.) for 10 min to transport the deposit of polycrystalline GaN which has been deposited on the SiO mask and recrystallize it from the GaN deposited on the openings of the SiO 2 mask and silicon which is perfectly oriented with respect to the substrate.
• a 2 ⁇ m thick deposit of GaN follows the recrystallization step.
• the thickness deposited by HVPE is between 300 and 1000 ⁇ m. The separation of the thick layer of GaN and the sapphire substrate is observed after HVPE growth. Only a few traces of silicon remain on the rear face of the self-supporting nitride layer; these traces can be removed by chemical attack.
• Example 8 Use ELO (bands) and Sapphire plane substrate R
• a self-supported substrate of gallium nitride is produced according to the method of the invention.
• the starting substrate consists of the following stack: a layer of silicon of 1 ⁇ m deposited on a layer of AIN of 50 nm deposited on a layer of GaN oriented in the direction A (l l-20) of 2 ⁇ m on a sapphire substrate (Al O 3 ) oriented in the direction R (10-12) 430 ⁇ m thick and 2 "in diameter.
• the layer of AIN serves as a protective barrier between the layer of silicon and the layer of GaN which can react together and degrade (diffusion of silicon in GaN).
• a 200 nm SiO 2 layer which will serve as a mask is deposited on the silicon layer. Patterns formed by bands a few microns wide separated by several microns ( typically 5 ⁇ m / 5 ⁇ m) are revealed in the SiO 2 layer by a standard photolithography step and a chemical attack by BOE for 3 min. Then a chemical attack on the silicon layer by KOH at 80 ° C. for 10 min is used to etch the unmasked silicon layer up to 'to the AIN layer (with the same pattern as that defined by photolithography). A first step of regrowth of gallium nitride is made by EPVOM at the openings of the silicon layer from the AIN layer.
• GaN deposition is done to obtain a continuous layer before growth by HVPE using ELO growth.
• the thickness of GaN deposited is 2 ⁇ m.
• This ELO regrowth step allows a reduction in the density of dislocations and extended defects by at least an order of magnitude in the GaN layer.
• the thickness deposited by HVPE is 800 ⁇ m.
• the separation of the thick layer of plane GaN A and the plane sapphire substrate R is observed after HVPE growth. Only a few traces of silicon remain on the rear face of the self-supporting nitride layer; these traces can be removed by chemical attack.

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